Animals are people's friends. But many wild animals are facing the ____ (危险) of dying out, because the environment that they are living has ____ (变化) greatly. Their living area has become ____ (小) than before because of ____ (污染) and the ____ (发展) of cities. They have no room to live in ____ (除了) the zoo. And many of the wild animals now can't find enough food to eat. At the same time, man is killing animals for their fur and meat. Now the situation is serious. So we should do something to ____ (保护) the animals. For example, we should set up some nature reserves so that animals can live ____ (自由) and stop people from ____ (杀死) animals. Of course a ____ （健康的） environment which has fresh air, clean water and green grass is also important for animals. Only in this way can we save them.